1. Field of the Invention:
The present invention relates to a method and a system for throwing carbon dioxide collected from combustion exhaust gas or the like into the deep sea.
2. Description of the Prior Art
The problem of warming up of the earth due to increase of a carbon dioxide gas concentration in the atmosphere has been being discussed over the world, and as one of countermeasures for this problem, there is an idea that the increase of a carbon dioxide gas concentration in the atmosphere is suppressed by industrially collecting carbon dioxide from combustion exhaust gas or the like and throwing it into the deep sea.
This idea is based on the fact that while the sea water in the surface layer of the ocean is held in contact with the atmosphere and is closely related to the atmosphere because of existence of its movement such as waves, tides and the like, since movement of the sea water in the portion deeper than about 100 m is very little and its communication with the sea water in the surface layer is little, it is presumed that if collected carbon dioxide is appropriately thrown into the deep sea, the carbon dioxide would not come out into the atmosphere over a long period or substantially semipermanently. Also, the idea is based on the fact that carbon dioxide of the amount several tens times as much as that in the atmosphere is present in a resolved state in the deep sea water, and so the influence in the event that the artificially thrown carbon oxide is added to this resolved carbon dioxide, is presumed to be faint.
FIG. 4 is a general conceptional view showing one example of the prior art method in which carbon dioxide is transported on the sea by means of ships and is then thrown into the deep sea.
In a heat power station 1, combustion exhaust gas containing carbon dioxide gas is generated from a boiler, and after carbon dioxide gas has been separated and collected from the exhaust gas it is solidified in a carbon dioxide gas collecting and processing apparatus 2. In other words, solid carbon dioxide (commonly called "dry ice") is produced. The temperature of this solid carbon dioxide is about -78.degree. C. under the atmospheric pressure as shown in FIG. 2, and it is temporarily stored in a solid carbon dioxide storage warehouse 3. Then, the solid carbon dioxide is loaded on a solid carbon dioxide transport ship 4, and is transported on the sea up to a predetermined sea region, where it is thrown down out of the ship. The specific gravity of the thrown solid carbon dioxide is about 1.5, and so it sinks due to its own gravity and reaches to the deep sea. The transport ship 4 returns to the original quay after throwing, and it performs transportation and throwing of solid carbon dioxide repeatedly.
FIG. 5 is a flow chart showing a process of producing solid carbon dioxide from carbon dioxide gas. Carbon dioxide gas 11 is compressed at 12 by means of a compressor and thereafter it is cooled and condensed at 13 into liquefied carbon dioxide 14. If this is subjected to adiabatic expansion at 15 by making it spout from a nozzle, about 30-60% of the liquefied carbon dioxide would evaporate, but the remaining liquefied carbon dioxide would become snowflake-shaped solid carbon dioxide 17 due to removal of the evaporation heat, and this is press-molded at 18 into solid carbon dioxide (commonly called "dry ice").
However, the throwing of carbon dioxide into the deep sea in the prior art as explained above, has the following shortcomings:
1. In the case of solidifying collected carbon dioxide, as compared to the case of liquefying it, the installation becomes expensive, and a lot of power for operating the installation becomes necessary. Furthermore, regarding the loading work onto a ship and the like, handling of solid carbon dioxide is troublesome as compared to the case of liquefied carbon dioxide.
2. Solid carbon dioxide thrown down out of a ship would evaporate furiously due to contact with the sea water, and a part of the evaporated carbon dioxide would escape into the atmosphere. In other words, there is a loss of carbon dioxide in the midway of throwing into the deep sea. PA1 3. There is an evaporation loss of carbon dioxide during a loading work onto a ship and during transportation, and furthermore, there is a fear that throwing down into a sea region other than a contemplated throwing sea region may be executed easily against the contemplated schedule. Therefore, and also as a result of the shortcomings described in the preceding two numbered paragraphs, it was difficult to precisely know when, where and by what amount throwing into the deep sea of carbon dioxide was executed. PA1 1. The state of carbon dioxide to be loaded on a ship is a liquefied state, and there is no need to solidify carbon dioxide. In addition, the state of carbon dioxide upon a work of loading on a ship is also a liquefied state which can be easily handled. PA1 2. As the carbon dioxide to be thrown into the deep sea passes through a throw-in pipe until it reaches to the deep sea, it would be never lost in the midway. PA1 3. An evaporation loss of carbon dioxide during the work of loading on a ship and during transportation on the sea is not present, and the route for throwing liquefied carbon dioxide into the deep sea is limited to within the deep sea throw-in pipe.